Mucociliary clearance of inhaled particles from the tracheobronchial tree is an important defense mechanism of the lung. A failure of this clearance mechanism in disease probably results in retained mucous secretions and a predisposition to pulmonary infection. Circumstantial evidence indicates that airway secretion of ions, water, and mucus is an important factor in determining the rate of mucociliary clearance. Because the normal and abnormal physiology of these important secretory processes is only partially known, my proposal is to study the interrelationships among them. Prior investigation during the tenure of this proposal, showed that there is a predominant active movement of chloride directed toward the dog tracheal lumen and a lesser active Na+ movement in the opposite direction. Also, we obtained data that is consistent with Na-coupled electrogenic Cl-secretion in this epithelium. Further, we have begun to characterize the kinetics of mucous glycoprotein secretion by dog trachea using radioactive markers. All of these prior studies have employed intact tracheal tissue, in vitro. The use of intact tissue to study the physiology of airway secretion has certain inherent limitations related to cellular complexity of the tracheal epithelium, which renders it difficult to determine the functional contribution of individual cell types. In preliminary studies, we have developed a method in cats to isolate submucosal gland cells from the surface tracheal epithelium. In the proposed studies, we plan to refine our efforts and to isolate individual viable serous and mucous cells from the cat trachea. We plan to grow cells in monolayers in order to characterize the electrical and ion transport properties of the cells employing Ussing's short-circuit technique. Finally, we will employ several methods to characterize biochemically the macromolecular secretory products and responses of these cells.